Gasoline engines are considered more economical and longer lasting that there glow counterparts. When they don't start, they can be trying for the most seasoned modeler.
If your Engine won't
start:
(1) - Make sure the Switch is turned "ON".
(2) -
If it uses a battery for ignition, make sure it is fully charged.
(3)
- Prime and Choke the Carburetor according to the Owner's
Manual.
(4) - Check that it is full of fresh Gas. (gas oil mix)
(5) - Return Lo/Hi carburetor needles back to factory settings.
(6) - Replace
the Spark Plug with a new one.
If it runs,
but poorly:
(1) - If it uses a battery for ignition, make sure it is fully charged.
(2) - Make sure the Choke is turned "OFF".
(3) -
Make sure the Gas is fresh. (gas oil mix)
(4) - Return Lo/Hi carburetor needles back to factory settings.
(5) - Replace the Spark Plug with a new
one.
There are three Basic things you need, to have an Engine
run:
Proper Compression, Proper Spark, and Proper
Fuel.
Compression can be tested with a gauge similar to the one that checks
your car tires. It will have a tapered rubber tip that presses against
the Spark Plug hole, or a threaded tip that screws into the Spark Plug
hole. You flip your engine over to get a reading.
You may know you have a
compression problem by the effort required to flip your engine through it's compression cycle. If it suddenly flips very easy, you probably have lost
some compression. This can be caused by various problems, most of which
require an experienced mechanic. He/she can also test the compression
for you. Adding a little oil through the spark plug hole and trying again may improve the compression during this test.
Spark
is delivered to the tip of a Spark Plug to ignite the gas inside the
cylinder. You can test for Spark by grounding the metal threads of the
Plug against the Engine while you gently flip the propeller. You should see a
spark jump at the end of the plug.
All this assumes that the spark plug
is good, the battery (if equipped) is charged, the spark plug wire is attached, and the Switch turned "ON". If you
have No Spark, try a new Plug and/or battery. If you still have no Spark and the wire
appears to be good and the switch is turned on then back to the "Experienced
Mechanic".
Fuel:
Here, more can go wrong than you can imagine. Always make sure the tank is
full of FRESH fuel.
Next,
remove the Gas Line from the Carburetor that goes to the Gas Tank. Put a
clean nipple and extension over the vent line to the tank.
When you blow in the nipple, gas
should squirt out of the disconnected Gas Line. If not; you have a
plugged Fuel Filter or clunk inside the Tank.
If the Gas Line is long enough
to allow it, cut 1/2" off the end when you reconnect it to the
Carburetor. Better yet; replace it.
Next we will discuss the disassembly of the carburetor.
The top two photos are typical of
Carburetors from 2-cycle gasoline engines.
The lubrication comes from 3 or 4 ounces of special 2-cycle oil
which is mixed with 1 gallon of gasoline by the operator. These are
different views of the popular Walbro Carburetor, showing the Valve Cover
and Fuel Pump Cover.
Top Left photo shows the bottom of the Carburetor which gets bolted to the
Engine-Intake with the Gasket shown, and allows the fuel-air mixture to
enter the Cylinder. It's ignited by the Spark Plug which creates an
internal explosion and makes power by causing rotation of the
Crankshaft.
Inside the round throat, you can
barely see the brass "Butterfly" which is a Valve that determines how much
fuel/air mixture is allowed into the Cylinder. This Butterfly is about the
size of a Penny. The big silver Screw allows access to the Valve
Diaphragm.
At the left is the throttle arm. This arm is connected to the engine servo to adjust the engine speed from idle/stopped to maximum RPM (wide open throttle). At top-left and bottom-right are Gas Inlets which carry gas from
the Tank to the Carburetor.
Top Right photo shows the Choke Butterfly and the 4 screws that hold the
cover on the Fuel Pump diaphragm chamber. The brass shaft at the top-left
is moved by the Choke Lever to control the amount of additional gas used
on cold-startups. The Screw in the center of this Butterfly allows its
removal which releases the Choke Shaft for
disassembly.
The throttle Butterfly is
similarly retained. These two Butterflies are connected to the servos that allow the operator to choke and throttle the
Engine with the transmitter.
Bottom-Left photo shows a K10-WAT Walbro Carburetor Kit which costs about
$8.00 including the 2 pieces of Gas Line which are different diameters to
fit the different diameter (why?) Gas Inlets! The bottom row shows the
Needle Valve parts, Filter Screens, and Welch Plugs.
Bottom-Right photo shows a close up of the Penny with the needle valve Rocker, a
"C"-Ring Retainer, and a Screen so tiny it looks like the cutout for the
hanger hole in the plastic bag. If you are not aware that this tiny part
is in the kit, it can easily be lost.
Disassembly:
Lay out the Carburetor parts as
you remove them so you can reassemble them in reverse order. A
7-compartment pill box is handy for this.
1 - Remove the large machine screw
from the center of the Valve Cover.
2 - Remove the Valve Cover.
3 - Remove the rubber Valve /
Gasket assembly
4- Remove the 4 small screws at
the corners of the Fuel Pump Cover.
(it has a raised dome
with a hole at the edge)
5 - Remove the Fuel Pump Diaphragm / Gasket
assembly.
Metering pump has a round metal plate with a
1/8" long pin in the center. This Pin operates the Needle Valve through
the Rocker
When replacing or reinstalling the tiny Needle
Valve Spring, it has no desire to "take its seat". In fact, when it's
compressed into working position, it may very well take flight never to
be seen again. A simple wooden toothpick can make you the
boss.
Put the toothpick through the Rocker into
the Spring as shown above. Then press the whole assembly into place as
you tighten the screw. It should be noted that first you should have
started the screw a thread or two.
Be sure the "Y" Yoke of the
Rocker is placed in the groove at the top of the Needle Valve, as shown
above.
If your Rocker has no hole above
the Spring, it may be best to take your Carburetor to a small engine repair shop
which is experienced in dealing with flying springs.
Once you have cleaned and reassembled the carburetor, it is now ready to be reconnected to the engine and the engine started.
It's helpful to know that 4
common problems are inexpensive and within the realm of a determined
do-it-yourself modeler
Storage is bad news for
Gasoline Engines! If they have to be stored, they are best stored indoors where it is warm, and
there is no sunshine. Plastic parts may become brittle, stretch, or
shrink. Gas Tubing and Carburetor Diaphragms may develop pinholes or
lose their elasticity.
ABOVE ALL: Don't leave Gasoline
in a engine for extended periods of time!! The gas will evaporate and
leave behind a residue of "varnish" that will coat and plug up
everything it touches. That's VERY bad news for a Carburetor and its
tiny Jets and passages.
Instead, drain the gas out,
start it up, and work it or let it idle until it runs out of gas. Then
put a teaspoon of 2-cycle Oil in the Spark Plug hole and slowly flip the engine over 3 or 4 times. This will coat the moving parts with oil and
protect them from corrosion and rust.
Spark Plugs: Inexpensive and easy to replace. Remember to never over-torque them.
Muffler: Easy to clean with engine flush, a wire brush, and compressed air.
Gas lines: Inexpensive and not too difficult to
replace
Carburetors: May only need to be adjusted. Kits are usually under
$10.00 and not all that difficult. But be aware that Kits may not
include instructions.
